Field of the Invention
The invention relates to an arrangement for supplying electric traction motors in a rail vehicle with electrical energy, where the arrangement includes at least two internal combustion engines. Provided for these at least two internal combustion engines is one associated electrical machine each for the generation of electrical energy, in which the electrical machine is coupled mechanically to the internal combustion engine so as to be driven by the internal combustion engine when the electrical machine is operating in generator mode. In this manner, a first and a second internal combustion engine combination at least are formed. The at least one electric traction motor of the rail vehicle is connectable electrically with at least one electrical machine by at least one traction connection. The invention further relates to a method for supplying electric traction motors in a rail vehicle with electrical energy, in which at least two internal combustion engines are driven each in combination with an associated electrical machine so that at least a first and a second internal combustion engine combination are operated. At least a first of the electrical machines generates, in a first operating state of the machine during generator mode of the respective electrical machine driven by the internal combustion engine, alternating current used for operating at least one electric traction motor. At least a second of the electrical machines, in a second operating state of the machine, is supplied with alternating current by a second machine power converter associated with it and drives the internal combustion engine associated with it.
The rail vehicle may, for example, be a locomotive. The invention is not restricted to that, however. Rather, the rail vehicle may, for example, also be a train unit.
In the rail vehicle, the electrical energy generated by the internal combustion engines in particular is not only available for supplying the at least one traction motor but also for supplying other electrical consumers. In particular, the other electrical consumers are so called auxiliaries that while not generating traction directly may be essentially necessary particularly for the driving mode of the rail vehicle. Auxiliaries may be defined generally in that they are supplied with electrical energy from the usually available direct current link by a separate auxiliaries inverter or a plurality of dedicated auxiliaries inverters. Examples of auxiliaries are, e.g., fans and other cooling devices which cool the internal combustion engines, the traction motors and/or other devices required for the driving mode (for example, power converters). In addition, a brake assembly is required for the driving mode and therefore components of the brake assembly such as air compressor belong to the auxiliaries. Other examples of auxiliaries are a fire extinguishing system of the rail vehicle, electronic devices for controlling the operation of the rail vehicle, battery chargers, heaters required at least temporarily for the driving mode, for example, window heater of the front window, and/or lighting equipment in the driver's compartment. Optionally, differentiated from the auxiliaries can be electrical installations which are merely provided for the comfort of the passengers such as, for example, lights in the vehicle compartments. These electrical installations are usually supplied with electrical energy in trains via the so called train bus bar. The train bus bar is not linked to the direct current link via the auxiliaries inverter or another of the auxiliaries inverters but by a dedicated inverter.
Description of Related Art
As is known from prior art, the electrical energy generated by the electrical machines can be fed in this invention as well into a direct current link via at least one rectifier (hereinafter: generator rectifier, because alternating current generated by the generator is rectified). Connected to the direct current link are typically several inverters which in turn generate the alternating current on the required electrical voltage level or in the required electrical voltage range that is needed for the consumers and systems connected to the alternating voltage. Additional to the inverters, provided at their direct current side can be direct power converters and/or transformers on their alternating voltage side, in order to change the voltage level. Other electrical converters may also be connected, either directly or indirectly, to the direct current link. Furthermore, except the auxiliaries aforementioned, other electrical consumers such as, for example, electrical installations provided for the comfort of the passengers such as lighting, air-conditioner and information systems, can be supplied with electrical energy from the direct current link, for example, via another inverter than those auxiliaries required for the driving mode.
For example, connected to the direct current link are: a plurality of traction motors of the rail vehicle via one or several traction inverters; a train bus bar via an additional converter, or directly; auxiliaries required for the driving mode via an auxiliaries inverter. Furthermore, additional converters can be connected to the link, for example, for the purpose of converting to heat excess energy fed into the link during the braking of the rail vehicle. An example of such an arrangement is described in WO 2009/077184 A1.
Since in the case of the present invention, more than one internal combustion engine is provided and respectively at least one electrical machine is coupled with the internal combustion engine, it is possible that only a part of the available electrical machines generates electrical energy whereas another part of the electrical machines will simultaneously operate as motor, particularly to drive the associated internal combustion engine in idle mode. The advantage of this is that the fuel supply to the internal combustion engine can be switched off. Alternately, it is also possible that at least one of the internal combustion engines runs only at low speed and so only little electric power is generated by the associated electrical machine or machines which, e.g., does not contribute or hardly contributes to an appreciable extent to the electric power fed into the direct current link.
A plurality of internal combustion engine/machine combinations therefore enables a partial load operation of the rail vehicle, i.e., an operation in which not the maximum possible electric power is needed. Consequently, partial load operation is understood to mean an operation in which the mechanical power of only a part of the internal combustion engines suffices to provide the required electric power. In addition to a reduction of the fuel consumption of the internal combustion engines, the partial load operation also has the advantage that the noise stress on the environment is much lower. For example, four internal combustion engine/machine combinations can be provided, in which preferably every combination can be operated independently of the other combinations either in idle mode or at the optimal power point. Optionally, more than two operation modes can be set for every combination, for example, additionally to the two operating modes mentioned, one operation with medium power of the electrical machines operating as generator.
In particular, as regards the further possible features of an arrangement with several internal combustion engine/machine combinations, reference is hereby made to the international patent application with the application number PCT/EP 2012/052705 which was submitted on Feb. 16, 2012. In particular, the entire content of that application is hereby included in this application by reference.
Electrical auxiliaries provided additionally to the electric traction motors and supplied with electrical energy from the direct current link include, in particular, such auxiliaries required—as aforementioned—for the driving mode of the rail vehicle. So when the auxiliaries inverter by which these auxiliaries are connected electrically with the direct current link fails or is switched off, the driving mode cannot be continued. This applies even if the direct current link and the supply of the traction motors from the link may still be functioning.
One, several or all of the internal combustion engine/machine combinations can be switched off so that, at a given time, it will be necessary to start one or several switched-off internal combustion engine/machine combinations. Particularly the internal combustion engine of the combination must be started, for which appropriate energy is needed. In the case of the present invention, the start of at least one internal combustion engine is performed by means of the associated electrical machine in that the electrical machine drives the internal combustion engine that is coupled to it mechanically. Particularly from a defined minimum speed of the internal combustion engine, the fuel supply to the internal combustion engine can be started so that the internal combustion engine starts working by itself. From that time, the internal combustion engine is started, even if the starting process may continue until the internal combustion engine attains a speed at which it can operate permanently without load without stopping running and is ready at any time to increase its speed and also operate under load. That speed is usually referred to as idling speed. Particularly, the internal combustion engine can, from the time at which it is working by itself, no more or only additionally be driven by the associated electrical machine, and from that or a later point in time, conversely, drive the electrical machine. At idling speed, the internal combustion engine drives the electrical machine which, however, does not or only marginally supply an electrical load with energy. When the speed increases further the internal combustion engine increases the power by which the electrical machine generates alternating current so that electrical consumers can be supplied with electrical energy by the electrical machine.
Expediently, the energy for the start of at least one of the internal combustion engines is obtained from an energy store of the rail vehicle, particularly an electrical or electro-chemical energy store, particularly the vehicle battery. The start of several internal combustion engines and also the frequent repetition of starting processes after turning off internal combustion engines (for example, in a partial load operation, see above) stresses the energy store of the vehicle significantly. To prevent exhaustion of the energy store, the storage capacity of energy store can be increased. However, this requires higher cost and/or an increase of the weight and construction volume of the energy store; but the energy store can also comprise units distributed in the vehicle.
It is common practice to increase the voltage level at the output of the energy store (e.g., 110 V DC) by a voltage transformer in order to provide sufficient voltage for starting the internal combustion engines. For example, a machine inverter supplied with direct voltage from the energy store and the voltage transformer, respectively, to supply the electrical machine with alternating current, is designed for a direct current of the order of 750 V or of 1 kV.
It may happen that the direct power converter fails and therefore no internal combustion engine can be started so that the rail vehicle is not in running order. This can be prevented in that at least one second, redundant voltage transformer is provided. However, this again increases the manufacturing cost, the construction volume and the weight.